实体框架核心可以为空的外键

Question

我无法获取外键值可能为null的实体列表.

型号:

public class Company
{
    [Key]
    [Required]
    public int Id { get; set; }
    [Display(Name = "Company Name")]
    public string CompanyName { get; set; }
    [Display(Name = "Main Phone")]
    public string LandPhone { get; set; }
    [Display(Name = "Fax")]
    public string FaxPhone { get; set; }
}

public class Contact
{
    [Key]
    [Required]
    public int Id { get; set; }
    [Display(Name ="First Name")]
    public string FirstName { get; set; }
    [Display(Name = "Last Name")]
    public string LastName { get; set; }
    [EmailAddress]
    public string Email { get; set; }
    [Display(Name = "Mobile Phone")]
    public string MobilePhone { get; set; }
    [Display(Name = "Office Phone")]
    public string LandPhone { get; set; }
    [Display(Name = "Fax")]
    public string FaxPhone { get; set; }
    public string Title { get; set; }
    public int CompanyId { get; set; }
    [ForeignKey("CompanyId")]
    public Company Company { get; set; }
}

当我尝试获取所有列表Contacts并且其中一个CompanyId在我的数据库中具有空值时,它将跳过Contact它返回的列表中的值.例如,查询var contacts = _context.Contacts.Include(c => c.Company).ToList();仅返回下表中的Josh Stone:

联系表

我正在使用Entity Framework Core 1.0.0.任何帮助将是真诚的感谢.

Answer 1

假设它确实回归玛丽,你会期望她的CompanyId是什么？我怀疑是null(它还能是什么？),在这种情况下你的模型是错的, public int CompanyId { get; set; } 应该是 public int? CompanyId { get; set; }